During the course of metallurgical operations, especially the refining of ferrous metals, namely iron and steel, it is frequently necessary to monitor the condition of the melt at a location below the surface thereof.
Such monitoring operations can take the form of a measurement of a parameter of the melt, e.g. its temperature, or the form of a sampling of the melt, i.e. the withdrawal of a portion thereof for subsequent analysis.
Such monitoring may be carried out fairly frequently and is utilized to follow the refining operation and to ensure optimum refining conditions for the highest quality of steel to be produced.
In order that the monitoring be effective, it is important that the samples be representative and taken at the same level or place, i.e. that the sample be withdrawn repeatedly at the same depth of immersion. Even small differences in the level at which the sample is withdrawn can result in errors with respect to the representativeness of the sample, the homogeneity of the product and variations in the refining process and other parameters of the product.
It is thus desirable that temperature measurements, for example, always be made at the same level if they are to be meaningful and any change of temperature is to represent significantly the progress of a refining process, and similarly, that the samples be withdrawn in succession from precisely the same location.
Under the rigorous conditions under which such measurements and sampling must be taken, i.e. extremely high temperatures, evolution of fumes, spattering, turbulence, it is impossible to rely upon an operator to visually control the depth of the sampling or measuring probe.
Consequently, the art has resorted to a mechanization of the sampling or measuring process whereby the descent of a measuring or sampling probe into the bath of molten metal, the duration for which the probe is immersed in the bath and the retraction of the probe from the bath are all controlled by an appropriate mechanism or control system.
For example, in automatic probe installations known heretofore, the descent of the probe is generally arrested at the same position with respect to a fixed reference. The disadvantage of this system, of course, is that it is not amenable to use with various receptacles of different depths or capacities or even shapes since the surface of the bath may be different in each case and the position at which the probe stops may not be meaningful for one or another type of receptacle.
Furthermore, even for a given receptacle the effective use of this system requires that the level of the bath surface always be the same. The level of the surface of the bath, however, is a function of a number of factors, including the quantity of metals charged, the introduction of additives, the tapping of metal or slag which can cause the surface level to vary from refining process to refining process and thereby prevent effective use of this earlier system.
Another system, attempting to overcome these disadvantages, is known from the open German application DE-OS 2,455,670 which utilizes a contact detector fixed on the probe carrier and which terminates the descent of the probe when the detector comes into contact with the superficial surface of the bath.
This detector is generally disposed at a fixed distance from the end of the probe, this distance corresponding to the depth of immersion.
While this arrangement overcomes a problem arising from variations in the position of the surface of the bath, it introduces a number of new problems. For example, it requires the mounting of an auxiliary element, namely the detector, on the side of the probe which may not be convenient, may create mechanical problems with the probe and certainly introduces new operations which can delay the sampling.
Generally, the detector can only be affixed at a given distance from the end or head of the probe so that the assembled apparatus can be used only for a single depth of immersion. The versatility of the arrangement is drastically limited by the fact that one cannot select the depth of immersion at will.
Furthermore, the detector is destroyed at each immersion of the probe into the bath, thereby requiring its replacement.